Investigation of H2S Diffusion in Transcritical and Supercritical Water: A Molecular Dynamics Simulation Study

In supercritical water (SCW) gasification technol-ogies, H2S is one of the important intermediate products. Studying the self-diffusion coefficient of H2S in subcritical water and SCW can help us better understand the mass transfer characteristics. In this work, we used the molecular dynamics method to simulate the diffusion behavior of H2S in the H2S-H2O system and calculated the self-diffusion coefficient of H2S under different conditions (pressure: 235-280 atm, H2S molar concentration: 1-5%, temperature: 600-1173 K). The result shows that the molar concentration and pressure of H2S have little effect on its self -diffusion coefficient, but temperature and water density have a greater effect on it. In addition, the self-diffusion activation energy of the supercritical region of H2S is only 32.58% of the subcritical region. Finally, we fitted new parameters of the empirical equation to predict the self-diffusion coefficient of H2S in the H2S-H2O system, whose mean relative error in the supercritical region is 3.05%.